This invention relates to Laser hardening and, in particular, to a method of high resolution thick film material patterning.
The prior art is replete with methods for providing thick film patterns such as resistor and conductor patterns for microelectronic circuitry on switchable substrates. Various thin film methods are known such as evaporation, sputtering, and photo resist etching to provide electrical patterns. Thick film techniques are also known such as silk screening a conductive ink onto the substrate in a desired pattern, fixing the substrate, and then laser trimming the pattern to the desired specifications. This process requires a chamber containing suitable gases or other compounds maintained under the right condition for processing. Merely heating the silicon by itself will not give the desired result. As another example, electrically conducting patterns can be deposited on silicon subsrates by selectively directing a laser beam of suitable power onto the silicon surface to heat it locally and precipitate a metal conductive coating in a pattern corresponding to the heated portions of the surface. Various applications of pattern hardening of material onto a substrate are also disclosed in the following references.
U.S. Pat. No. 4,061,799 to Brewer discloses a method of patterning styrene-diene block copolymer electron beam resists. A thin film of styrene-diene block copolymer is applied to a support and is subjected to an electron beam scan in a vacuum which irradiates part of the film according to a programmed pattern. The exposed section becomes insoluble in a solvent while the unexposed area remains soluble and is therefore dissolved and removed. The desired pattern remains.
U.S. Pat. No. 4,063,949 to Uhlig et al. discloses a process utilizing laser beams for the preparation of planographic printing forms. A recording material comprising a support layer of anodically oxidized aluminum and a recording layer is irradiated with a laser beam, thereby rendering the exposed portions of the recording layer insoluble. The non-irradiated portions can be removed by washing with a developer liquid.
U.S. Pat. No. 4,159,414 to Suh et al. discloses a method for forming electrically conductive paths. A substrate, comprising a polymer material having a metal compound and a metal oxide incorporated as a filler, is heated by a laser beam at desired locations. The temperature is sufficient to reduce the metal compound to its elemental state, thus forming the desired electrically conductive paths.
U.S. Pat. No. 4,467,026 to Ogawa discloses a process for drawing patterns with extremely fine features in the production of VLSI, LSI and IC Systems. An electron beam is used to write a pattern over a resist layer on a wafer and the resist layer is exposed by X-rays.
U.S. Pat. No. 4,477,324 to Cline discloses a technique for making eutectic fine wire arrays. Arrays are made by directionally solidifying the component of a eutectic alloy system as a thin film and consequently removing at least one of the phases.
There are various difficulties with the prior art methods. For example, it is very difficult if not impossible to screen a pattern onto an uneven surface. Also, thin film processes can be relatively expensive because of materials and techniques. On the other hand, thick film techniques usually offer relatively low resolution. Also, methods using a laser to burn away all but the desired pattern require the relatively costly and excessive use of a high power laser and the process is relatively slow.
It is an object of the present invention, therefore, to provide a new and improved method of laser forming resistors, conductors and insulators, in particular, in providing a relatively inexpensive method of providing patterns on uneven surfaces using thick film materials and yet provide relatively high resolution. Further advantages of the present invention will become apparent as the following description proceeds, and the features characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.